Method and instrumentation for vertebral interbody fusion

ABSTRACT

A method and instrumentation particularly adapted for disc space preparation from an anterior approach to the spine. In one aspect, an expandable template is provided having guides to guide a cutting device for bilateral formation of openings in the disc space. In another aspect, an improved guide member is provided for guiding a cutting tool. Still further, the invention provides an improved double barrel guide sleeve with a central distraction extension and lateral non-distracting extensions. Optionally, the guide sleeve includes windows and covers to selectively cover the windows. An improved reamer with an internal chamber and optional modular coupling is also provided. A depth stop is provided to selectively engage a tool shaft and a guide sleeve to control tool penetration into the disc space. A method of using the disclosed instruments is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a division of U.S. patent application Ser.No. 09/287,917, filed Apr. 7, 1999, which claims the benefit of U.S.Provisional Application No. 60/081,206, filed Apr. 9, 1998, nowabandoned, all of which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to surgical proceduresfor spinal stabilization and more specifically to instrumentationadapted for inserting a spinal implant within the intervertebral discspace between adjacent vertebra. More particularly, while aspects of theinvention may have other applications, the present invention isespecially suited for disc space preparation and implant insertion intoa disc space from a generally anterior approach to the spine.

[0003] Various surgical methods have been devised for the implantationof fusion devices into the disc space. Both anterior and posteriorsurgical approaches have been used for interbody fusions. In 1956, RalphCloward developed a method and instrumentation for anterior spinalinterbody fusion of the cervical spine. Cloward surgically removed thedisc material and placed a tubular drill guide with a large foot plateand prongs over an alignment rod and then embedded the prongs intoadjacent vertebrae. The drill guide served to maintain the alignment ofthe vertebrae and facilitated the reaming out of bone material adjacentthe disc space. The reaming process created a bore to accommodate a bonedowel implant. The drill guide was thereafter removed following thereaming process to allow for the passage of the bone dowel which had anouter diameter significantly larger than the reamed bore and the innerdiameter of the drill guide. The removal of the drill guide left thedowel insertion phase completely unprotected.

[0004] More recent techniques have advanced this concept and haveprovided further protection for sensitive tissue during disc spacepreparation and dowel insertion. Such techniques have been applied to ananterior approach to the lumbar spine. In one approach, a unilateraltemplate has been provided to evaluate the space in the disc space. Forbilateral implant placement, the template entire device must be rotatedand visually aligned to approximately 180° from the previous position.Thus, there is the chance for operator error in rotating the device tothe correct position. Further, there is little guidance to ensure properalignment of cutting instruments extending through the template.

[0005] One approach to provide such alignment is the use of a guide wireextending through a cannulated cutting instrument, such as a trephine.However, for instruments with hollow cutting heads, there is typicallyno engagement between the inner walls of the hollow cutting head and theguide wire. Thus, the guide wire may bend between the portion extendinginto the tissue and the guide wire entrance into the cannula of theinstrument. As a result, the hollow cutting head may not remain insubstantial alignment with the guide wire, resulting in improper openingformation. Therefore, there remains a need for improved guidingmechanisms for cutting instruments.

[0006] Once an initial opening or openings have been made in the discspace, the height of the disc space is normally distracted toapproximate the normal height. Typically, a first distractor with aheight estimated by CT or MRI examination is inserted. If additionaldistraction is required, the first distractor is removed and a second,larger distractor is inserted. However, since the positioning of thedistractors is usually performed without the benefit of protective guidesleeves, the switching of distractors increases the potential for damageto neurovascular structures and may increase the time of the procedure.

[0007] For bilateral procedures, a double barrel sleeve may be insertedover a pair of previously placed distractors with a central extensionextending into the disc space to maintain distraction. One limitation onguide sleeve placement is the amount of neurovascular retraction thatmust be achieved to place the guide sleeves against the disc space. Forsome patients, a double barrel sleeve may not be used because there isinsufficient space to accept the sleeve assembly. Further, although thedistal end of the sleeve assembly may be configured to engage thevertebral surface, if material has been removed from the disc space,there is the potential that adjacent neurovascular structures mayencroach on the working channels in the disc space, resulting in damageto these structures caused by contact with instruments. Whilevisualization windows on the guide sleeve may assist in bettervisualization of procedure steps and verifying unobstructed workingchannels prior to tool insertion, the windows themselves may allowtissue to come into contact with instruments in the working channels.Thus, there remains a need for guide sleeves requiring reducedneurovascular retraction for proper placement and providing greaterprotection to adjacent tissue.

[0008] With guide sleeves in place, the disc space and end plates may beprepared for receipt of an implant. Typically, cutting instruments areadvanced to remove disc material and bone. Such operations may be timeconsuming since it is often necessary to adjust depth stop equipment andto remove the instruments to remove cutting debris. Since it isdesirable to shorten the time of the operative procedure, there remainsa need for improved cutting instruments and depth stop mechanisms.

[0009] While the above-described techniques are advances, improvement isstill needed in the instruments and methods. The present invention isdirected to this need and provides more effective methods andinstrumentation for achieving the same.

SUMMARY OF THE INVENTION

[0010] The present invention relates to methods and instrumentation forvertebral interbody fusion. In one form, the method contemplates gainingaccess to at least a portion of the spine, marking the entrance point orpoints in the disc space, creating an initial opening in the disc spacethrough a template, distracting the disc space and positioning an outersleeve defining an interior working channel adjacent the disc space. Ina preferred embodiment, the template can be inserted in a reduced sizedconfiguration, with a first portion engaging the tissue. The templatemay then be manipulated to a larger configuration for bilateralinsertion procedures by movement of a second portion, withoutrepositioning the first portion. Additionally, a template according tothe present invention may include trephine guides that accommodate avariety of different diameter trephine cutting heads. Specifically,trephines according to the present invention may include an upper shafthaving a uniform diameter regardless of trephine cutting head diameter.Thus, the upper guides of the template maintain the trephine in axialalignment regardless of whether the lower guide engages the trephinehead. In another aspect of the invention, an improved guide member isprovided to maintain alignment of cutting instruments.

[0011] Once an initial opening or openings have been defined in the discspace, a distractor may be inserted to distract the disc space to thedesired height. Various distractors according to the present inventionmay be used to distract the disc space. One such distractor has a firstposition that provides a first working distraction height in the discspace and a second position that provides a greater second workingdistraction height. Should the first working distraction height beinsufficient, the distractor according to the present invention may berotated one quarter turn to create a second greater distraction heightin the disc space. Additionally, in a further preferred aspect of theinvention, a modular distractor mechanism according to the presentinvention may be configured to accept many different rotatabledistractor tips and may releasable engage the tips such that adistractor tip may be left in the disc space while permitting withdrawalof the distractor tool shaft. With such a configuration, a singledistractor tool shaft may be use with various tips, thereby limiting thetotal number of complete distractor instruments required. Additionally,distractor tips may be made of radiolucent material that will notinhibit x-ray imaging of the disc space. Such distractor tips mayinclude radiographic markers to indicate the ends and/or outer edges ofthe device and markers to indicate the rotational alignment of thedistractors in the disc space.

[0012] Once the desired distraction of the disc space has been achieved,the handle of the distractor may be removed and an outer sleevepositioned over the distractor. For a bilateral approach, one or both ofthe distractors may be left in position and a double barrel sleevepositioned over the distractors and advanced toward the disc space. Afurther step that may be performed in a preferred embodiment is toselect a removable distal tip for the outer sleeve that matches theheight of disc space distraction and the diameter of the implant. Thus,an outer sleeve may be used with interchangeable distal tips toaccomplish the insertion. Whether single or double, the sleeve isadvanced until the leading distractor portion of the outer sleeve isadjacent the disc space. If necessary, a driving cap may be positionedover the proximal end of the outer sleeve. The outer sleeve is thendriven into position, preferably with a spike or series of spikesengaging vertebrae adjacent the disc space.

[0013] Although various sleeves are known in the art, in a preferredembodiment, outer sleeves according to the present invention have areduced width portion adjacent the distal end to limit the amount ofretraction of the surrounding vascular and neural structures requiredfor the procedure. In a preferred form, a double barrel sleeve assemblyincludes a central distraction flange having a first height and anopposing pair of lateral extensions having a second height, less thanthe first height. The lateral extensions provide protection fromencroachment of tissue into the working area in the disc space. Afurther aspect of a preferred embodiment includes the provision ofvisualization windows along the outer sleeve for visual access to theinterior working channel while instruments are in the working channel.Various combinations of windows are disclosed to accomplish the desiredvisualization. While visualization is desirable, having openings in theouter sleeve may allow surrounding vessels and tissue to migrate intothe working channel of the outer sleeve. Tissue and vessels present inthe working channel may be damaged by insertion and removal of the tools(often with cutting edges) or during use of those tools. Thus, thepresent invention contemplates covers over the windows that may beselectively opened for visualization and closed to prevent tissue andvessel infiltration. Additionally, the covers or the outer sleeve may betransparent to allow visualization through the windows without removingthe covers or directly through the sleeve. In a similar manner, an imageguidance system such as that available under the tradename STEALTH maybe used in conjunction with the present system to monitor theadvancement and positioning of instruments and implants. Even withoutthe use of an imaging system, the present invention discloses the use ofmanually adjustable depth stop that may be used to control the steps oftrephining, reaming, tapping, and dowel insertion. The term dowel isused in a broad sense throughout the disclosure and is intended toencompass dowels made of bone, metallic cages and other implants usedfor interbody fusion regardless of shape or material of construction.

[0014] One aspect of the present invention comprises an outer sleevewith a visualization window disposed adjacent a distal end and a coverremovably covering the window. In one preferred embodiment, the coverincludes a flange adjacent the distal end to mobilize vessels and othertissue away from the ends of the outer sleeve. In one form, the cover isslidably disposed on the upper surface of the tube or tubes to coveronly the upper windows. In another form, the cover is slidablypositioned on the tube to cover the upper and lower windows of the tube.

[0015] In yet another aspect, the outer sleeve has a double barrelconfiguration. The bone engagement end of the outer sleeve includes afirst flange having a first height sufficient to maintain distraction.Preferably, the bone engaging end also includes a pair of opposinglateral extensions having a second height less than the first height.The lateral extensions are intended to inhibit lateral encroachment oftissue into the working area in the disc space but are not limited tomaintain distraction.

[0016] Another aspect of the present invention comprises an adjustablestop mounted on a tool shaft. The stop is selectively engageable withthe tool shaft at a plurality of locations along the tool shaft by axialmovement of a collar to control the position of the stop engagingportions. With the collar in a first position, the engaging portions aredisengaged from the tool space. With the collar in a second position,the engaging portion is urged into engagement with the shaft. The toolshaft is sized to be received within an outer sleeve and the stop issized to prevent passage within the outer sleeve. Thus, the stop may beselectively coupled to the tool shaft to control the extent of toolshaft that may be received within the outer sleeve. Although notrequired, in one embodiment the stop includes a viewing window and thetool shaft includes markings, whereby the markings are calibrated toindicate to the user the extent of tool shaft extending beyond a distalend of the outer sleeve.

[0017] Still another aspect of the invention comprises a reamer with areaming head having a plurality of reaming apertures in communicationwith an internal channel. The internal channel extends within thereaming head and proximally along at least a portion of the reamershaft. The internal channel includes a proximal segment extendingnon-parallel to the longitudinal axis of the reamer shaft, wherebyreaming debris may be transferred to the exterior of the reaming shaft.

[0018] The present invention further contemplates a method for interbodyfusion comprising, positioning a template adjacent a fusion site,forming at least one initial opening in the disc space, distracting thedisc space, placing a distal portion of an outer sleeve into the discspace, the outer sleeve including at least one visualization window andcover removable disposed over the windows and visualizing the surgicalsite through the windows. Preferably, the method also includes removingthe cover to expose the window prior to visualization. Further, themethod may include the step of enlarging the opening with cutting toolsand may further include attaching an adjustable depth stop to the toolshaft prior to extension beyond the distal end of the outer sleeve.

[0019] Related objects and advantages of the present invention will beapparent from the following brief description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1a is a perspective view of an expandable template accordingto the present invention.

[0021]FIG. 1b is a side elevational view of the template of FIG. 1a.

[0022]FIG. 1c is front view of the template of FIG. 1a.

[0023]FIG. 1d is a top view of the template of FIG. 1a.

[0024]FIG. 1e is a bottom view of the template of FIG. 1a.

[0025]FIG. 1f is an enlarged perspective view of the engaging end of thetemplate of FIG. 1a.

[0026]FIG. 2a is a perspective view of the template of FIG. 1a in anexpanded condition.

[0027]FIG. 2b is a top view of the template of FIG. 2a.

[0028]FIG. 3a is a side view of another embodiment of an expandabletemplate according to the present invention with a trephine disposedtherein.

[0029]FIG. 3b is a top view of the expandable template of FIG. 3ashowing the locking mechanism.

[0030]FIG. 4a is a perspective view of a guide member and trephineaccording to the present invention.

[0031]FIG. 4b is an enlarged perspective view of a portion of FIG. 4a.

[0032]FIG. 5a is a perspective view of a distractor according to thepresent invention.

[0033]FIG. 5b is an enlarged front view of the tip of the distractor ofFIG. 5a.

[0034]FIG. 5c is an enlarged side view of the tip of the distractor ofFIG. 5a.

[0035]FIG. 6 is a perspective view of a guide sleeve assembly accordingto another aspect of the present invention.

[0036]FIG. 7 is a front view of the guide sleeve assembly of FIG. 6.

[0037]FIG. 8 is a side view of the guide sleeve assembly of FIG. 6.

[0038]FIG. 9 is a partial cross-sectional side view of a guide sleeveassembly with a removable tip.

[0039]FIG. 10 is a perspective view of a guide sleeve assembly with acover according to the present invention.

[0040]FIG. 11 is an end view of the guide sleeve assembly of FIG. 10.

[0041]FIG. 12 is a front view of one embodiment of a guide sleeve windowcover according to the present invention.

[0042]FIG. 13 is a front view of a guide sleeve assembly with the coverof FIG. 12 mounted thereon.

[0043]FIG. 14 is a perspective view of an engaging end of a guide sleeveassembly with another embodiment of a window cover according to thepresent invention.

[0044]FIG. 15a is a side view of a window cover.

[0045]FIG. 15b is an end view of the window cover of FIG. 15a.

[0046]FIG. 16a is still a further embodiment of a window cover inaccordance with the present invention.

[0047]FIG. 16b is an end view of the window cover of FIG. 16a.

[0048]FIG. 17 is an anterior to posterior view of a guide sleeveassembly with window covers according to FIG. 15 disposed thereon, theguide sleeve assembly is positioned in relation to a pair of adjacentvertebral bodies and blood vessels.

[0049]FIG. 18 is a partial cross-sectional top view of a guide sleeveassembly with only one window cover positioned thereon, a portion of theguide sleeve assembly extending into the disc space.

[0050]FIG. 19 is a side view of a hollow headed reamer in accordancewith another aspect of the present invention.

[0051]FIG. 20 is the reamer of FIG. 19 rotated 90 degrees about theshaft longitudinal axis.

[0052]FIG. 21 is an enlarged partial cross-sectional view of the head ofthe reamer of FIG. 19.

[0053]FIG. 22 is a side view of a clean out tool for use with the hollowreamer head of FIG. 19.

[0054]FIG. 23 is a top view of the clean out tool of FIG. 22.

[0055]FIG. 24 is a side view of a tap in accordance with the presentinvention.

[0056]FIG. 25 is a side view of a tap having a removable tap head inaccordance with another aspect of the present invention.

[0057]FIG. 26a is a side view of a reamer having a removable reamer headin accordance with another aspect of the present invention.

[0058]FIG. 26b is a partial cross-sectional view of the connectionmechanism of FIG. 26a.

[0059]FIG. 27 is a perspective view of a depth stop according to thepresent invention with the collar partially retracted to expose thelocking fingers.

[0060]FIG. 28 is a side view of the depth stop of FIG. 27.

[0061]FIG. 29 is a cross sectional view taken along line 29-29 of FIG.28.

[0062]FIG. 30 is a front view of the depth stop of FIG. 27 with thecollar fully extended.

[0063]FIG. 31 is a side view of an alternative embodiment of a depthstop in accordance with the present invention.

[0064]FIG. 32 is a partial side view illustrating the depth stop of FIG.31 in engagement in with a tool shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0066] The present invention relates to methods and instrumentation forperforming vertebral interbody fusion. Specifically, although aspects ofthe present invention may have other uses either alone or incombinations, the instruments and methods disclosed herein areparticularly useful for anterior lumbar interbody fusion. Provisionalapplication No. 60/081,206 filed Apr. 9, 1998 is incorporated herein byreference.

[0067] Referring now to FIGS. 1(a) through (f), there is shown anintraoperative template 10 for use in interbody fusion. Intraoperativetemplate 10 includes a central anchoring pin 12 and two supplementalanchoring pins 14 and 16. These pins are adapted to be driven intovertebral bodies or other tissue adjacent a disc space to anchor theintraoperative template 10 in the proper location. Template 10 includesan outer shaft 18 interconnected with handle 22 and an inner shaft 20disposed within outer shaft 18. Inner shaft 20 extends to encompass pin12. Outer shaft 18 is rotatable with respect to inner shaft 20. Disposedadjacent the distal end of template 10 are guide members 24 and 26connected to inner shaft 20 and outer shaft 18, respectively.Preferably, guide members 24 and 26 are substantially circular plateshaving an aperture therein. Guide members 24 and 26 define openings 28and 30, respectively, adapted to receive a trephine tool therethrough.Trephine guides 34 and 36 are positioned along outer shaft 18 and haveopenings 40 and 42, respectively, in alignment along axis 31 and aresized to receive a trephine tool shaft. In an alternative embodiment, itis contemplated that inner shaft 20 may be connected to guide member 26and outer shaft 18 may be connected to guide member 24.

[0068] In a first reduced size configuration for unilateral templatingand guiding, shown in FIG. 1a, guide members 24 and 26 are axiallyaligned along axis 31 with openings 28 and 30, respectively, in similaralignment. In this reduced size configuration, the expandable templatemay be inserted into the body through a relatively small opening and thetemplate may be used for unilateral templating and guiding of atrephine. In this position, a trephine may be guided through guides 34and 36 and guide members 24 and 26 to engage the tissue below. Moreover,referring to FIG. 3a, a trephine according to the present invention mayhave a uniform diameter along most of its shaft such that it is a closefit within guides 34 and 36. The close fit in guides 34 and 36 maintainsaxial alignment, while permitting trephine shaft rotation. Thus, asingle template 10 may be used with a variety of sizes of trephine headdiameters, provided the shaft has a substantially uniform diameter.

[0069] Referring now to FIG. 1a, handle 22 is connected to outer tube 18and may be rotated in the direction of arrow 32 to a bilateraltemplating and guiding position. This action rotates outer shaft 18 withrespect to inner shaft 20. Guiding member 26, guide 34 and guide 36 areconnected to outer shaft 18 and therefore rotate when handle 22 ismoved. In contrast, first guide member 24 is interconnected with innershaft 20 and remains stationary upon rotation of handle 22. As shown inFIG. 2a, handle 22 is rotated approximately 180 degrees to align secondtemplate 26 approximately 180 degrees from first template 24 and therebyexpand the template to its bilateral trephining position. Thus, atrephine procedure may be conducted along axis 33 through guides 34 and36 and second member 26 to cut an opening in the disc space. Axis 33 isspaced from axis 31 by a distance “D” representing the distance ofspacing of the midpoints between implants to be inserted. FIGS. 2a and 2b show the first and second templates rotated 180 degrees with respectto one another. FIG. 2b shows a top view of a bilateral templating andguiding configuration. In this expanded configuration, the outer edgesof guide members 24 and 26 define the total area necessary for placementof implants and instruments having a specific configuration and size.While in a preferred embodiment, cylindrical implants having diametersof 16 mm, 18 mm or 20 mm may be used, it is contemplated that otherdiameters may be used and other shapes such as, but without limitation,squares and rectangles.

[0070] Shown in dashed line in FIG. 2b is a groove 39 formed in guidemember 24 and projection 37 defined on guide member 26 and extendinginto groove 39. It will be understood that the engagement between groove39 and projection 37 maintains alignment and limits rotation to 180degrees. Thus, template 10 may be moved between the reduced sizeconfiguration and expanded configuration, but the groove and projectionengagement limit further movement and will provide a positive indicationof 180° rotation, thereby eliminating the requirement for visualalignment with the first position.

[0071] Referring now to FIG. 3a, there is illustrated a furtherembodiment of an expandable template according to the present invention.Template 600 is substantially identical to template 10 previouslydisclosed above, with the exception that template 600 includes a lockingmechanism 613. Expandable template 600 includes a handle 626 connectedto outer shaft 622. As in the previous embodiment, template 600 includesa first guide member connected to inner shaft 624 and a second guidemember 606 connected to outer shaft 622. First guide member 608 includesspike 612 and inner shaft 624 extends to form central spike 610. Outershaft includes guides 602 and 604. As shown in FIG. 3a, a trephine 601may be positioned through guides 602 and 604, and through guide member606. The cutting head 605 includes cutting teeth 611, a series of indexmarkings 607 and a window 609 to visualize the contents in the hollowinterior. Preferably, trephine 601 includes a central cannula 603extending from the handle to the cutting head.

[0072] A locking mechanism 613 is disposed between the inner and outershafts to prevent rotation. Referring to FIG. 3b, locking arm 614 ispivotally attached to inner shaft 624 by pivot pin 620. The locking armmay be pivoted to extend through slot 616 in the outer shaft and slot618 in the inner shaft. It will be understood that with locking armdisposed in the slots the inner and outer shaft will be prevented fromrotation. In a first locked position, the shafts are aligned as shown inFIG. 1a in the reduced size configuration. In a second locked position,the shafts are aligned as shown in FIG. 3a in the expanded bilateraltemplating configuration. It will be understood that the expandable,rotatable template of the present invention permits insertion of thedevice through a smaller opening than would have been permitted with afixed relation double trephine opening template. Further, the expandabletemplate may be locked in either a unilateral or a bilateral position.Locking engagement in the bilateral position insures accurate bilateralplacement with consistency that would not be readily achievable with aunilateral template particularly where the surgeon must reposition thedevice by visual alignment. Subsequently, the device may be rotated toan expanded configuration suitable for trephine guiding to formbilateral openings without removing the instrument.

[0073] In use, access to an anterior portion of the spinal column isachieved by known method. Blood vessels, particularly the aorta, venacava, and branches thereof are mobilized to provide space for bilateralimplant placement. With the template in the reduced size configurationof FIG. 1a, the template is inserted into the body and advanced untilthe pins are disposed adjacent a disc space. The circumference of thetemplate guide member is selected to the circumference needed forbilateral placement of a pair of implants. More specifically, the areaof the guide members of FIG. 2b closely approximate the area needed forplacement of the double barrel guide sleeve disclosed herein, see forexample FIG. 11. Central pin 12 is disposed centrally between theintended location of the implants. In either the unilateral or expandedbilateral condition, the template may be disposed adjacent the discspace to measure the space available for implant and instrumentplacement. If the space appears too small, a smaller sized template maybe inserted to evaluate the space. In the bilateral condition, thetemplate approximates the area needed for implant and instrumentplacement. Vessels disposed within the templated area may need to bemobilized outside the area or an alternative implant size or approachmay be utilized. Further, osteophytes that appear within the templatedarea may be removed to prepare for engagement with a guide sleeve. Oncethe area is cleared, the pins are inserted into the tissue of the discspace and/or adjacent vertebra to anchor the template, therebymaintaining its position during subsequent steps. As shown in FIG. 3a, atrephine is inserted into the guides and through the guiding members.The trephine is cuttingly advanced into the disc tissue to form anopening therein. The trephine may then be at least partially removedfrom the template to permit movement between the first and second guidemembers. If a lock mechanism is used, the locking arm must be moved toan unlocked position and the handle rotated to rotate the upper guidemember to the expanded bilateral templating position. The trephine isreinserted and advanced through the upper guide member to form a secondopening aligned with and offset a distance D from the first opening.Thus, the template permits controlled bilateral opening formationthrough an expandable and collapsible template. The template may becollapsed into its reduced size form and withdrawn after completion ofthe trephining operation.

[0074] Referring now to FIGS. 4a and 4 b, there is shown a furtherguiding device according to the present invention. Guiding member 450includes an elongated shaft 430 having a substantially uniform diameterover most of its length. Shaft 430 includes a distal portion adapted forguiding a cutting instrument having a hollow cutting head. The distalportion of shaft 430 includes distal end 432 having a sharpened tip 434adapted to penetrate tissue, specifically tissue disposed in the discspace. Distal end 432 includes markings 444 which indicate the extent ofshaft 430 disposed in the disc space. Although guide member ispreferably formed of stainless steel, other bio-compatible materials arecontemplated. Specifically, shaft 430 may be formed of a radiolucentmaterial and markings 444 may be radiopaque. Adjacent distal end 432 isenlarged portion 436 having a diameter substantially greater than theshaft diameter. Enlarged portion 436 is adapted to prevent furtheradvancement of guiding member 450 into the tissue and to guide thecutting of the cutting tool. Enlarged portion 436 preferably includes aplanar surface 442 substantially perpendicular to the longitudinal axisof shaft 430. A substantially spherical surface 440 is disposed adjacentplanar surface 442. This is followed by a tapering conical surface 438that is adapted to align the cutting head over enlarged end 436. It willbe understood that the internal surface of cutting head 426 definingopening 428 engages the transition line 448 between spherical surface440 and taper surface 438. The diameter of transition line 448substantially matches the internal diameter of cutting head 426 toprovide a close fit for maintaining alignment.

[0075] In use, guide member 450 is inserted into the body with distalend 432 fully inserted into the tissue of interest, preferably disctissue although other uses are contemplated. Cutting tool 420 isadvanced over guide member 450 with shaft 422 in substantial alignmentwith shaft 430 extending through channel 427. While a trephine isillustrated, other cutting tools such as, but without limitation,reamers and non-rotary cutting tools may be used with guide membersaccording to the present invention. Cutting teeth 425 are positionedadjacent enlarged portion 436 and are advanced until the cutting teethsurround the enlarged portion. It will be understood that if cuttingteeth are offset with respect to enlarged portion 436, the teeth willengage a portion of conical surface 438 and thereby be urged intoalignment. Enlarged portion 436 is received within chamber 428 andcutting teeth 425 are advanced along distal portion 432 until conicalsurface 428 abuts internal conical surface 429 to prevent furtheradvancement. The assembly may be withdrawn with the cut tissue impaledby distal portion 432. The tissue may be removed from chamber 428 byadvancing the guide member with respect to the cutting head such thatthe enlarged portion urges the tissue out of the hollow interior. Thismay be particularly helpful where the cutting tool is used to extract abone graft. The depth of cutting teeth penetration may be adjusted byplacement of the enlarged portion. Additionally, while only a singleenlarged portion is shown, more than one may be positioned on the shaftto further adjust the guide member depth and cutting depth of the tool.

[0076] Referring now to FIGS. 5a-c, there is shown a disc spacedistracter 50 according to one aspect of the present invention.Distractor 50 includes a proximal end 53 configured as an enlarged endfor engagement with a conventional Hudson connection on a T-handle (notshown). Shaft 54 is joined with a distracter tip 56. While an integralshaft and head are shown, head 56 may be removably attached to shaft 54.One such removable attachment is more fully disclosed in provisionalapplication No. 60/081,206 incorporated herein by reference. Distractertip 56 is designed such that it can be inserted in a disc space toestablish a first working distraction height 72 (see FIG. 5b), which isless than a second working distraction height 70 (see FIG. 5c). Morespecifically, distracter tip 56 has a rounded leading edge 62 thatextends to opposing inclined surfaces 58 and 59 which extending moreproximally blend into substantially planar opposing surfaces 60 and 61,respectively. Planar surfaces 60 and 61 extend in parallel alignmentalong the longitudinal axis of the distracter to establish height 72. Itwill be understood that the inclined surfaces 58 and 59 cooperate toease insertion into the disc space and to initially distract the discspace to at least a height 72. If first height 72 is sufficient, furtherprocedures as known in the art may then be carried out to accomplishimplant insertion. Alternatively, rounded leading edge 62 permits thedistractor to be inserted to directly achieve second distraction height70.

[0077] In an alternative aspect, should first height 72 be insufficient,head 56 may be rotated a quarter turn, or 90 degrees, to the positionshown in FIG. 5c. Rounded surfaces 64 and 66 engage the bone to urge itapart and into a second larger distracted height 70. It will beunderstood that utilization of a distracter tip as disclosed in thepresent invention, permits a two-height distraction of the disc spacethat may be carried out with a single instrument and without removingthe instrument from the disc space. This offers an advantage to thesurgeon of a single instrument offering multiple useful distractionheights. Thus, a surgeon may initially believe a disc space will need afirst amount of distraction. After insertion of the distractor, thesurgeon may discover that further distraction is required. In thissituation, a distractor according to the present invention allowsfurther disctraction without instrument withdrawal. Moreover, distractorhead 56 limits the number of instruments that must be made available tosurgeon to accomplish a surgical procedure by providing two workingdistraction heights on a single tool. Specifically, but withoutlimitation, the distraction heads may be formed with first heights 72ranging from 6 mm to 12 mm and second heights ranging from 7 mm to 13mm. Preferably, heights 70 and 72 vary by 2 mm increments. Morepreferably, height 72 is 8 mm and height 70 is 10 mm. In another form,height 72 is 10 mm and height 70 is 12 mm. Other variations may beutilized that provide multiple working distraction heights thatapproximate the disc height in a normal spine.

[0078] Referring now to FIG. 6, there is shown a double-barrel guidesleeve assembly 100 having a first sleeve 140 connected to a secondsleeve 142. Sleeves 140 and 142 each define working channels 130 and 132extending in a substantially unobstructed manner from the proximal end102 to distal end 104. Assembly 100 includes upper windows 106 and 108formed in sleeves 142 and 140, respectively, that are adapted forengagement by a removal tool. The sleeves also include lower elongatedvisualization windows 110 and 112.

[0079] Adjacent distal end 104, the material thickness along the outeredge of each tube 140 and 142 is reduced in order to provide a smallercross-sectional area for the sleeve assembly as well as a reduced widthextending transverse to the longitudinal axis of assembly. The reducedcross-sectional area and smaller width reduces the amount of retractionof vessels adjacent the disc space that would be required without thereduction. Side wall 114 is shown as an indication of the reducedthickness of the device in the distal area 104.

[0080] Distal end 104 includes a central distracting flange 116 whichmay be inserted into the disc space to achieve or maintain a height H1of distraction between two vertebral bodies. Lateral flanges 118 and 120also extend partially into or adjacent to the disc space. However, in apreferred embodiment, lateral flanges 118 and 120 have a height H2 thatis less than height H1. Thus, they do not provide distraction of thedisc space but are provided primarily to protect surrounding vessels andneurological structures from damage during the procedures. Although thatis the function of the lateral flanges in the preferred embodiment, itis contemplated that they could be sized to provide distraction withinthe disc space in conjunction with central flange 116. Additionally,distal end 104 includes spikes 122, 124, 126, and a fourth spike whichis not seen in the view of FIG. 10. These spikes may be urged into thebone of the adjacent vertebral bodies to hold the double-barrel guidesleeve 100 in a fixed position relative to the vertebral bodies. It willbe understood that windows 110 and 112 provide the medical staff withthe opportunity to visualize the instruments as well as the openings inthe disc space and vertebral bodies, without entirely removinginstrumentation from guide sleeve 100.

[0081] Referring more specifically to FIG. 7, double-barrel guide sleeve100 is shown in a front view to further illustrate an additional aspectof the invention. Opposite vertebrae engaging end 104, the guide sleevehas a width W1 approximately twice the diameter of one of the sleeves.Adjacent vertebrae engaging end 104 of the sleeve, each of the outerportions of the sleeves has a reduced wall thickness at side walls 114and 113. The walls are not entirely flat but have a substantiallygreater radius of curvature (see FIG. 11) giving the appearance ofsubstantially flat walls but providing a reduction in wall thicknessover a greater area and tapering to the full wall thickness at thetermination of side walls 113 and 114. The reduced wall thickness on thelateral portion of each tube reduces the overall width of the device toa width W2. The reduction in width decreases the amount of retractionthat vessels in the area must be moved. The desirable reduction in widthis accomplished with little reduction in the strength of the devicesince much of the structural integrity, particularly resistance to axialcompression during insertion of the sleeves, is carried by the muchthicker central portion where the two sleeves are joined to each other.Preferably, the central portion may have a thickness equal to two tubewall thickness.

[0082] As a further alternative, FIG. 9 shows that guide sleeve assembly190 may be provided with removable barrel tips 191 having differentdistraction heights, lateral extensions, or spike patterns. Barrel tipsmay also have different diameters corresponding to the placement ofimplants with different diameters. Removable tips 191 may be held inplace by any of a variety of known connection mechanisms. However, in apreferred embodiment, guide sleeve assembly 190 includes a pair ofopposing flexible fingers 192 and 193 having projections 194 and 195,respectively. Projections 192 and 193 on the flexible fingers extendinto grooves 196 and 197, respectively, defined in the removable tip. Tolimit proximal movement of tip 191 during insertion, tapered surface 198abuttingly engages shoulder 199 and the central portion between theupper guide tubes. Use of a removable tip according to the presentinvention not only allows use of interchangeable tips to suit a specificapplication, it also permits removal of the outer sleeve after placementin the body. With only tip 101 in place, the posterior aspect of thedisc space or spinal canal may be more easily visualized and accessed.

[0083] Referring now to FIGS. 10 and 11, there is shown a furtherembodiment of a double-barrel guide sleeve similar in most respects toouter sleeve 100 of FIG. 6. The further embodiment of FIG. 12 differsfrom that of FIG. 6 in that guide sleeve 100 included only a singleelongated visualization window for each sleeve. In double-barrel guidesleeve 150, each sleeve has a total of four windows, two on an uppersurface and two on a lower surface. Thus, as shown in FIG. 10, windows152, 154, 156, 158 provide the surgeon with the opportunity forvisualization along the majority of each working channel. The back sideof guide sleeve 150 has a similar configuration.

[0084] Guide sleeve 150 is used in a similar fashion to the outer sleeve100. In a preferred embodiment, outer sleeve 100 is provided with acover 160 having a length 162 sufficient to cover all four windowsdisposed on at least one side of the device. Cover 160 is provided toprevent possible damage to tissues which may invade the working channelthrough the windows and be damaged by the operation, insertion orremoval of tools in the working channels. It is contemplated that cover160 may be transparent to allow visualization directly through the coveror that it could be opaque, requiring that the cover be repositionedprior to visualization. It is further contemplated that the cover mayhave a length 162 sufficient to extend over all the windows on one sideand it may be able to selectively cover either proximal windows 156 and158 or all of the windows. Leading edge 163 is tapered to prevent damageto tissue, particularly when moving forward to cover the windows. Thetaper should urge the tissue out and away from the guide sleeve.Further, cover 160 includes a dip 171 substantially following thecontour between the pair of guide sleeves.

[0085] Although other attachment mechanisms are contemplated, as shownin FIG. 11, cover 160 is held in place by retaining pin 170 connectedthrough cover 160 to a lower dovetail portion 172. Dovetail portion 172is slidable along a dovetail groove defined by grooves 168 and 169defined within the outer body of guide sleeve 150.

[0086]FIGS. 10 and 11 show one embodiment of a cover for slidably andselectively covering a plurality of windows in outer sleeve 150. FIGS.12 through 16b illustrate yet further embodiments of a cover which maybe displaced to expose underlying windows in one of the double-barreltubes. Further, although the covers are disclosed for use with doublebarrel assemblies, it is contemplated that they may be used with singletube guide sleeves without undue modification. In the furtherembodiments, the working channel and visualization windows of one barrelmay be exposed while a cover remains in place on the alternate barrel.

[0087] Referring to FIG. 12, partially cylindrical cover 182 consists ofelongated portions 183 and 185 which are sized to cover underlyingvisualization windows. The elongated portions are retained on the guidesleeve by connectors 184 and 186 that are sized to extend around theexterior of the outer tube and guiding portion 188. It is contemplatedthat connectors 184 and 186 may engage a cover portion on the oppostieside of the guide sleeve identical to that shown in FIG. 12. While cover182 is disclosed as having elongated members 183 and 185 interconnected,it is contemplated that each of the covers 183 and 185 could be separateto allow visualization of the windows only on an upper or lower surfaceof the working tube without opening the opposing window.

[0088] Referring to FIGS. 14 through 16b, there are shown still furtherembodiments of window covers according to the present invention. FIG. 14shows a cover 510 that covers approximately 200° of a single sleeve 502of a guide sleeve assembly 501 similar to that of FIG. 6. The coverincludes an internal passage 515 and is slidable along sleeve 502. In afurther aspect, cover 510 includes an enlarged flange 512 adjacent boneengaging end 504. Tapered surface 513 extends between flange 512 and theouter diameter of cover 510. Referring to FIGS. 15a and 15 b, cover 514includes a flange 516 that extends along the entire leading edge of thecover. The cover extends in a partial cylinder lacking material overangle 517.

[0089] Angle 517 is approximately 160°, thus material extends aroundapproximately 200° of the cylindrical shape. It will be understood thatcovers 510, 514, and 520 may be configured to have material extendingless than 200° around the cylinder to allow rotation of the cover inrelation to a guide sleeve such that the cover may be rotated to uncovera window. Thus, for covers 510 and 514, the flanges may continue to holdthe vessels away from the guide sleeve even when moved to allow accessthrough one of the windows.

[0090] An alternative embodiment shown in FIGS. 16a and 16 b does notinclude the enlarged flange 512. Cover 520 has a uniform end 524 anddefines an internal channel 522 adapted to receive a guide sleeve.However, in certain surgical procedures it is desirable to use theembodiment having the flange to protect closely adjacent vessels and tourge them away from the distal end of the guide sleeve where it might bepossible to contact instruments disposed therein. Without the use of acover, the outer sleeves may not match the shape of the surface of thevertebral body thereby allowing the potential for contact betweeninstruments in the outer sleeves and closely adjacent vessels. This isparticularly dangerous when operating close to the vena cava and aorta.However, as shown in FIGS. 17 and 18, the flanges on the covers act as aretractor to urge the vessels away from the outer sleeves.

[0091] Referring more specifically to FIG. 17, guide assembly 550 isillustrated as being inserted into a disc space D between two adjacentvertebra V1 and V2. Disposed adjacent the guide assembly 550 are vessels562 and 560 graphically representing portions of the aorta or vena cava.Covers 556 and 558 are mounted on guide tubes 552 and 554, respectively.Flanges on the covers, shown more clearly in FIG. 15a, urge the vesselsaway from the guide tube and more importantly, away from workingchannels 553 and 555 were tools would be inserted. Vessels 560 and 562are most closely adjacent guide tubes 552 and 554 near V₁. Thus, lateralextensions on the guide assembly may be insufficient to prevent contactbetween vessels and tools in all applications.

[0092] Referring now to FIG. 18, there is shown a top view of a guideassembly 580 positioned in the disc space adjacent a vertebral body 591.The guide assembly 580 includes a central distractor 582 and lateralextensions 584 and 586. Spikes 590 and 592 may be inserted into the boneof the vertebral body. For the purposes of illustration, cover 596 hasbeen positioned over a first guide tube, while guide tube 595 withwindow 593 remains uncovered. Bone engaging end 594 does not entirelyconform to vertebra surface 589, thus allowing the possibility of vesselmigration into the working channels. Cover 596 with flange 598 urgesvessel 599 away from the engagement between bone engaging end 594 andbone surface 589. In contrast, vessel 597 is positioned adjacent theinterface between the guide tube and bone, resulting in the potentialfor vessel migration into the working channel via the space between thebone engaging end 594 and bone surface 589. Thus, covers according tothe present invention may also be useful to further retract vessels awayfrom the interface between the bone engaging end of the guide assemblyand the bone surface.

[0093] Referring now to FIGS. 19 through 21, there is shown a reamer 200according to the present invention. FIG. 20 shows the reamer 200 of FIG.19 rotated 90 degrees. Reamer 200 includes a cutting head 202 havingcutting flutes 203 with troughs 205 disposed therebetween. Disposed intrough 205 is an aperture 204 extending to interior channel 209. Aseries of apertures 204 are defined in the cutting troughs andcommunicate with interior channel 209. The interior of cutting head 202is hollow and forms interior channel 209. Interior channel 209 has afirst portion with side walls substantially parallel to the longitudinalaxis and a second portion defined by side walls extending at an angle tothe longitudinal axis. Preferably the second portion extends at anon-orthogonal angle to permit easy cleaning. The second portion isconnected to aperture 208 formed on the outer surface of the shaft andspaced from the cutting head. It will be understood that aperture 208permits material cut by reaming head 202 to move through the interiorchannel 209 to exit at aperture 208. Moreover, the reduced diametersegment 211 defines an area between the shaft and outer sleeve wheredebris from the cutting operation may collect prior to removal of thedevice. This collection area has a length 214 in a preferred embodiment,although it is understood that this could be extended to increase thevolume of material that may be collected. This configuration permitscompletion of the cutting operation without a requirement to remove thereamer to clean the collected debris. Additionally, the debris may bevisualized through outer sleeve windows for evaluation.

[0094] Reduced diameter shaft 211 extends proximally to tapered region210 which expands to a larger diameter guiding portion 212. Taperedregion 210 assists ease of insertion and guiding of the shaft of thereamer within an outer working sleeve as previously disclosed. Largerdiameter guiding portion 212 is sized to have a reasonably close fitwithin an outer working sleeve to permit rotation of the device, yetlimit the amount of transverse movement within the tube to insureaccurate reaming within the bone. Reamer 200 may thereby be guided by aguide sleeve. Shaft 216 interconnects the proximal end to the enlargedarea 212.

[0095] Disposed on shaft 216 are a series of numbers 218, which indicatethe depth the reamer extends into the bone beyond the edge of acooperable guide sleeve. As can be appreciated from examining FIGS. 19and 20, the numbers are displayed in a stepped arrangement around thecircumference of shaft 216. This stepped arrangement permits each numberto be larger, in the preferred embodiment three times larger, than theycould be if all numbers were listed in a single column along the device.Thus, this arrangement permits easy visualization of the number by thesurgeon despite the small incremental adjustment of the device,preferably 1 mm increments. Extending more proximally along the shaft216 are a series of grooves 221 which are adapted to engage a depth stopmechanism (described further below) to adjust the reaming depth of thedevice. On the proximal end 220 is a Hudson-type connection forengagement with a T-handle or other type of handle.

[0096] Referring now to FIGS. 22 and 23, there is shown a clean out tool700 adapted for use with the hollow reamer head described above. Cleanout tool 700 includes a head 702 having a diameter substantiallymatching the diameter of internal chamber 209. Clean out tool 700includes a flexible portion 704. Flexible portion 704 is connected toshaft 708 which is connected to handle 706. Flexible portion 704 allowsthe device to enter through opening 208 in the reamer and force materialout open end 201 of the reamer head as end 710 is advanced. This is animprovement over hollow head reamers that do not provide a clean outchannel.

[0097] Referring now to FIG. 24, there is shown a thread tap 230 fortapping a reamed out bone space. Tap 230 includes a cutting head 232,and a reduced diameter shaft 233 adjacent head 232 for providing spacearound the shaft between the outer tube for the collection of debrisfrom the tapping operation. A tapered surface 234 extends to anincreased outer diameter area 236. As previously explained with respectto reamer 200, tapered surface 232 permits guiding of the tap within aguide sleeve and enlarged area 236 by providing a reasonably close fitwith the guide sleeve to maintain the axial alignment of tap 230. Tap230 includes incrementally stepped depth markings 240 and a Hudsonconnection 242 as previously disclosed with respect to reamer 200.

[0098] Referring now to FIGS. 25 through 26b, there are shown modularcutting tools joined to a shaft. FIG. 25 shows a shaft 250 releasablycoupled to tap head 252 by coupler 254. Similarly, shaft 250 is coupledto reamer head 256 by coupler 254. In FIG. 26a reaming head 256 may beremoved from shaft 250 at the connection 254. The reamer includes areaming head 256 having only six cutting apertures disposed around thehead and a hollow internal chamber connected to aperture 258. While anynumber of known connection mechanisms may be used, FIG. 26b shows theuse of an axially displaceable collar 260 to release balls 262 and 263from grooves 264 and 265 of the reamer head. Shaft 250 includes a hollowextension 268 having apertures 270 and 271 to hold balls 263 and 262,respectively. Collar 260 includes a reduced diameter portion 276 adaptedto urge balls 262 and 263 into grooves 264 and 265 to lock the cuttinghead and shaft together. Collar 260 may be axially displaced away fromthe cutting head to dispose an enlarged internal diameter portion 278adjacent the balls to allow them to disengage grooves 264 and 265,thereby allowing the cutting head to be disengaged from the shaft. Thesame mechanism may be used with a variety of cutting heads.

[0099] Referring now to FIGS. 27 through 31, there is disclosed a depthstop mechanism cooperable with the shaft of a tool and guide sleeve suchas previously disclosed. Such tools can include, without limitation, areamer, a tap, and an implant inserter. Depth stop 326 includes anenlarged circumferential abutment shoulder 330 adapted to engage theproximal end of an outer working sleeve to prevent further advancementof the stop and any interconnected shaft. Stop 326 further includesviewing windows 328 to permit visualization of depth markings on a shaftextending within the stop. Stop 326 includes a manually operated collar332 which may be axially displaced to allow flexing of fingers 334.Collar 332 is normally urged into an extended position by spring 342.

[0100] Referring specifically to FIG. 29, fingers 334 includeprojections 336 extending internally and bearing surface 337 extendingexternally. The internal projections 336 are configured for engagementwithin grooves 221 (FIG. 20) defined along a tool shaft of a workingtool, and bearing surface 337 is configured to engage collar 332.Additionally, each finger includes an external taper portion 339 adaptedfor engagement with bearing surface 340 of collar 332 to urge thefingers inwardly as the collar is advanced. It will be understood thatin a retracted position, bearing surface 340 of collar 332 will besubstantially disengaged from taper 339 and permit fingers 334 todisengage from groove 221 of a working shaft (FIG. 20). With collar 332in the extended position shown in FIG. 29, bearing surfaces 340 willbear against bearing surface 337 of each finger to urge projections 336into grooves 221 of a tool shaft. To release fingers, collar 332 may bemoved in the direction of arrow R until bearing surface 340 moves beyondtapered surface 339. The flexible fingers may then spring outward. Inthis manner, a user may quickly and easily disengage the lockingmechanism of the stop to advance or retract a working tool and thenre-engage the stop at the desired position. Preferably, distal end 333of collar 332 will extend beyond fingers 334 to limit the possibilitythat surgical staff may snag protective apparel on exposed fingers.

[0101] In a first embodiment shown in FIG. 30, collar 332 is retained onhousing 334 by retaining pin 342 extending into the housing and througha slot 344. Retaining pin 342 prevents rotation of collar 332 withrespect to housing 334. In an alternate embodiment shown in FIG. 31,collar 332 defines an L-shaped slot 346 which permits axial displacementof collar 332 with respect to body 334, as well as a slight amount ofrotation within the slot. It will be understood that the L-shaped slot346 permits the depth stop mechanism to be locked in a disengagedposition which permits free movement of the tool shaft through the depthstop. This is a desirable construction in some instances for easyremoval of the depth stop from the tool shaft, as well as forutilization of the tool without the constraints of a depth stopmechanism.

[0102]FIG. 32 shows a depth stop 326 engaged with a tool shaft havinggrooves 360 and marking 362 to show the depth of the distal end of thetool out of the guide sleeve 370. Abutment shoulder 330 is sized toengage the guide sleeve to prevent further movement. It will beunderstood that the depth of penetration may be adjusted between anumber of positions defined by engagement of the fingers 336 in grooves360 of the tool shaft. The adjustment is easily accomplished by axialmovement of collar 332. Engagement with the tool shaft is indexed by thespacing of grooves 360 on the tool shaft so the exact location of thestop may be easily known. The tool shaft may be rotated with respect tothe stop mechanism to display the appropriate depth numeral 362 inwindow 328.

[0103] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A distractor, comprising: a distraction headhaving a longitudinal axis and a first pair of opposed surfacesextending substantially along said longitudinal axis and defining afirst working distraction height approximating a normal disc spaceheight and a second pair of opposed surfaces extending substantiallyalong said longitudinal axis and defining a second working distractionheight approximating a second normal disc space height, said distractionhead rotatable between said first distraction height and said seconddistraction height by rotating the distraction head about saidlongitudinal axis.
 2. The distractor of claim 1, wherein said firstworking distraction height is 10 mm and said second working distractionheight is 12 mm.
 3. The distractor of claim 1, wherein said firstworking distraction height is 8 mm and said second working distractionheight is 10 mm.
 4. The distractor of claim 1, wherein said first pairof opposing surfaces are planar surfaces extending in a parallelalignment along said longitudinal axis.
 5. The distractor of claim 4,wherein said distractor head includes: a distractor tip having a roundedleading edge to permit insertion of said distractor head to directlyachieve said second working distraction height; and a pair of inclinedsurfaces extending from said leading edge to said first pair of opposingsurfaces.
 6. The distractor of claim 1, wherein said distractor headincludes rounded surfaces adapted to engage and urge bone apart to saidsecond distraction height during rotation.
 7. The distractor of claim 1,further comprising a shaft joined with said distractor head.
 8. Thedistractor of claim 7, wherein said shaft is integrally joined to saiddistractor head.
 9. A disc space distractor, comprising: a shaftextending along a longitudinal axis; a distractor tip joined to saidshaft; said distractor tip including a rounded leading edge, opposinginclined surfaces and substantially planar opposing surfaces; saidrounded leading edge extending to said opposing inclined surfaces; saidopposing inclined surfaces blending into said planar opposing surfaces;said planar surfaces extending in a parallel arrangement along saidlongitudinal axis to establish a first distraction height; saiddistractor tip further including opposing rounded surfaces defining asecond distraction height; wherein said distractor tip is rotatableabout said longitudinal axis to distract vertebrae between said firstdistraction height and said second distraction height; and wherein saidsecond distraction height is greater than said first distraction height.10. The distractor of claim 9, wherein said distractor tip is integralwith said shaft.
 11. A method of distracting adjacent vertebrae,comprising: defining a first disc space height between the adjacentvertebrae with a distraction head having a longitudinal axis; androtating the distraction head about the longitudinal axis to define asecond disc space height between the adjacent vertebrae.
 12. The methodof claim 11, wherein the second disc space height is greater than thefirst disc space height.
 13. The method of claim 11, wherein saidrotating includes turning the distraction head ninety degrees about thelongitudinal axis.
 14. The method of claim 11, wherein: the distractionhead has a first pair of opposed surfaces that extend substantiallyalong the longitudinal axis, the first pair of opposed surfaces define afirst working distraction height approximating the first disc spaceheight; the distraction head has a second pair of opposed surfacesextending substantially along the longitudinal axis and defining asecond working distraction height approximating the second disc spaceheight between the adjacent vertebrae said defining the first disc spaceheight includes supporting the adjacent vertebrae with the first pair ofopposed surfaces; and said rotating includes turning the distractionhead to support the adjacent vertebrae with the second pair of opposedsurfaces.
 15. The method of claim 11, wherein said defining the firstdisc space height includes inserting the distraction head between theadjacent vertebrae.